The study of kitty chromosomes shows that all female cats possess two X chromosomes. On the other hand the males have the X and Y patterns. The mother passes the X chromosome on to her kittens, and the father gives either the X or Y chromosome. How these two kitty chromosomes are combined will determine the gender of the kitten.

In all cats there found to be 19 pairs of kitty chromosomes. One set is inherited from the mother; the other set is from the father. These kitty chromosomes determine the sex of the offspring and can be either X or Y chromosomes.

The mother always passes on the X chromosome, but the male cat can only give an X or Y chromosome. The gender of the kitten will depend on which chromosome the father gives. The kitty chromosomes from the father also affect the fur color and pattern.

A male calico or tortoiseshell cat has two X and one Y chromosomes. All female cats have two X kitty chromosomes that contain genes creating the three calico pattern colors. A male calico or tortoiseshell has only one X chromosome. This X chromosome gives the fur color of orange or black. In the calico cat there is a gene for the white color of the calico pattern.

Sometimes a kitten has three chromosomes instead of the XX or XY chromosome pattern. This cat will have the XXY chromosome pattern and is always a male and sterile. A calico or tortoiseshell cat must have two XX chromosomes to get the fur colors.

In order for a cat to have a Calico coat, it must have the two fur color genes. These X chromosomes that the mother cat gives to the kitten. If the kitten somehow gets two X and a Y chromosome, it will be born sterile and the kitten will always be male.